Line scan imaging of objects transported on a conveying system typically requires that the optical components, e.g., sensing element of a camera, be parallel to the surface of the object that is being scanned. In conveyor applications, this forces the optical components to be mounted directly below the equipment, for bottom scanned images. However, the environment below the conveying system is full of airborne debris that is difficult to manage, which coats the camera optics and mirror. To this end, bottom scan applications require frequent cleaning, which over time degrades the mirrors and optical elements and hence eventually degrades the quality of the images acquired by the system.
To account for the airborne debris, previous efforts have focused on reducing the airborne debris. This includes shielding panels to protect the optical components. However, shielding panels are difficult to install, are costly and obstruct many of the components for maintenance. Another solution is to use transparent plates as viewing ports. These plates, though, become loaded with debris, typically get scratched and become hazy, and add cost. Another approach is to use vacuum or air knife systems. These systems require additional power, controls and maintenance, in addition to adding costs and contributing to noise within the facility.
Top scan applications, on the other hand, require the optical elements, e.g., sensing element of the camera, to be placed directly over the conveying system. Maintenance and adjustments are difficult to perform particularly while the objects are moving on the conveying system. In fact, with top scan applications, maintenance requires the conveying system to be stopped, or provide some means of safe access while the conveying system is running. There is also the issue of glare reduction, which can be reduced by angling the “scan line plane”. Such angling of the scan line plane, though, requires additional conveyor length for top scan applications; whereas, for bottom scanning applications, the angle reduces the effective viewing slot for light to pass through such that a wider gap between adjacent belts or other conveyances may be needed.